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[ Upstream commit d888c83fcec75194a8a48ccd283953bdba7b2550 ]
Jason Donenfeld reports that my commit 1c24a186398f ("fs: fd tables have
to be multiples of BITS_PER_LONG") doesn't work, and the reason is an
embarrassing brown-paper-bag bug.
Yes, we want to align the number of fds to BITS_PER_LONG, and yes, the
reason they might not be aligned is because the incoming 'max_fd'
argument might not be aligned.
But aligining the argument - while simple - will cause a "infinitely
big" maxfd (eg NR_OPEN_MAX) to just overflow to zero. Which most
definitely isn't what we want either.
The obvious fix was always just to do the alignment last, but I had
moved it earlier just to make the patch smaller and the code look
simpler. Duh. It certainly made _me_ look simple.
Fixes: 1c24a186398f ("fs: fd tables have to be multiples of BITS_PER_LONG")
Reported-and-tested-by: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: Fedor Pchelkin <aissur0002@gmail.com>
Cc: Alexey Khoroshilov <khoroshilov@ispras.ru>
Cc: Christian Brauner <brauner@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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[ Upstream commit 1c24a186398f59c80adb9a967486b65c1423a59d ]
This has always been the rule: fdtables have several bitmaps in them,
and as a result they have to be sized properly for bitmaps. We walk
those bitmaps in chunks of 'unsigned long' in serveral cases, but even
when we don't, we use the regular kernel bitops that are defined to work
on arrays of 'unsigned long', not on some byte array.
Now, the distinction between arrays of bytes and 'unsigned long'
normally only really ends up being noticeable on big-endian systems, but
Fedor Pchelkin and Alexey Khoroshilov reported that copy_fd_bitmaps()
could be called with an argument that wasn't even a multiple of
BITS_PER_BYTE. And then it fails to do the proper copy even on
little-endian machines.
The bug wasn't in copy_fd_bitmap(), but in sane_fdtable_size(), which
didn't actually sanitize the fdtable size sufficiently, and never made
sure it had the proper BITS_PER_LONG alignment.
That's partly because the alignment historically came not from having to
explicitly align things, but simply from previous fdtable sizes, and
from count_open_files(), which counts the file descriptors by walking
them one 'unsigned long' word at a time and thus naturally ends up doing
sizing in the proper 'chunks of unsigned long'.
But with the introduction of close_range(), we now have an external
source of "this is how many files we want to have", and so
sane_fdtable_size() needs to do a better job.
This also adds that explicit alignment to alloc_fdtable(), although
there it is mainly just for documentation at a source code level. The
arithmetic we do there to pick a reasonable fdtable size already aligns
the result sufficiently.
In fact,clang notices that the added ALIGN() in that function doesn't
actually do anything, and does not generate any extra code for it.
It turns out that gcc ends up confusing itself by combining a previous
constant-sized shift operation with the variable-sized shift operations
in roundup_pow_of_two(). And probably due to that doesn't notice that
the ALIGN() is a no-op. But that's a (tiny) gcc misfeature that doesn't
matter. Having the explicit alignment makes sense, and would actually
matter on a 128-bit architecture if we ever go there.
This also adds big comments above both functions about how fdtable sizes
have to have that BITS_PER_LONG alignment.
Fixes: 60997c3d45d9 ("close_range: add CLOSE_RANGE_UNSHARE")
Reported-by: Fedor Pchelkin <aissur0002@gmail.com>
Reported-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Link: https://lore.kernel.org/all/20220326114009.1690-1-aissur0002@gmail.com/
Tested-and-acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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commit e386dfc56f837da66d00a078e5314bc8382fab83 upstream.
Commit 054aa8d439b9 ("fget: check that the fd still exists after getting
a ref to it") fixed a race with getting a reference to a file just as it
was being closed. It was a fairly minimal patch, and I didn't think
re-checking the file pointer lookup would be a measurable overhead,
since it was all right there and cached.
But I was wrong, as pointed out by the kernel test robot.
The 'poll2' case of the will-it-scale.per_thread_ops benchmark regressed
quite noticeably. Admittedly it seems to be a very artificial test:
doing "poll()" system calls on regular files in a very tight loop in
multiple threads.
That means that basically all the time is spent just looking up file
descriptors without ever doing anything useful with them (not that doing
'poll()' on a regular file is useful to begin with). And as a result it
shows the extra "re-check fd" cost as a sore thumb.
Happily, the regression is fixable by just writing the code to loook up
the fd to be better and clearer. There's still a cost to verify the
file pointer, but now it's basically in the noise even for that
benchmark that does nothing else - and the code is more understandable
and has better comments too.
[ Side note: this patch is also a classic case of one that looks very
messy with the default greedy Myers diff - it's much more legible with
either the patience of histogram diff algorithm ]
Link: https://lore.kernel.org/lkml/20211210053743.GA36420@xsang-OptiPlex-9020/
Link: https://lore.kernel.org/lkml/20211213083154.GA20853@linux.intel.com/
Reported-by: kernel test robot <oliver.sang@intel.com>
Tested-by: Carel Si <beibei.si@intel.com>
Cc: Jann Horn <jannh@google.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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commit 054aa8d439b9185d4f5eb9a90282d1ce74772969 upstream.
Jann Horn points out that there is another possible race wrt Unix domain
socket garbage collection, somewhat reminiscent of the one fixed in
commit cbcf01128d0a ("af_unix: fix garbage collect vs MSG_PEEK").
See the extended comment about the garbage collection requirements added
to unix_peek_fds() by that commit for details.
The race comes from how we can locklessly look up a file descriptor just
as it is in the process of being closed, and with the right artificial
timing (Jann added a few strategic 'mdelay(500)' calls to do that), the
Unix domain socket garbage collector could see the reference count
decrement of the close() happen before fget() took its reference to the
file and the file was attached onto a new file descriptor.
This is all (intentionally) correct on the 'struct file *' side, with
RCU lookups and lockless reference counting very much part of the
design. Getting that reference count out of order isn't a problem per
se.
But the garbage collector can get confused by seeing this situation of
having seen a file not having any remaining external references and then
seeing it being attached to an fd.
In commit cbcf01128d0a ("af_unix: fix garbage collect vs MSG_PEEK") the
fix was to serialize the file descriptor install with the garbage
collector by taking and releasing the unix_gc_lock.
That's not really an option here, but since this all happens when we are
in the process of looking up a file descriptor, we can instead simply
just re-check that the file hasn't been closed in the meantime, and just
re-do the lookup if we raced with a concurrent close() of the same file
descriptor.
Reported-and-tested-by: Jann Horn <jannh@google.com>
Acked-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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[ Upstream commit b1b6b5a30dce872f500dc43f067cba8e7f86fc7d ]
For cancelling io_uring requests it needs either to be able to run
currently enqueued task_works or having it shut down by that moment.
Otherwise io_uring_cancel_files() may be waiting for requests that won't
ever complete.
Go with the first way and do cancellations before setting PF_EXITING and
so before putting the task_work infrastructure into a transition state
where task_work_run() would better not be called.
Cc: stable@vger.kernel.org # 5.5+
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Grab actual references to the files_struct. To avoid circular references
issues due to this, we add a per-task note that keeps track of what
io_uring contexts a task has used. When the tasks execs or exits its
assigned files, we cancel requests based on this tracking.
With that, we can grab proper references to the files table, and no
longer need to rely on stashing away ring_fd and ring_file to check
if the ring_fd may have been closed.
Cc: stable@vger.kernel.org # v5.5+
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull init and set_fs() cleanups from Al Viro:
"Christoph's 'getting rid of ksys_...() uses under KERNEL_DS' series"
* 'hch.init_path' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (50 commits)
init: add an init_dup helper
init: add an init_utimes helper
init: add an init_stat helper
init: add an init_mknod helper
init: add an init_mkdir helper
init: add an init_symlink helper
init: add an init_link helper
init: add an init_eaccess helper
init: add an init_chmod helper
init: add an init_chown helper
init: add an init_chroot helper
init: add an init_chdir helper
init: add an init_rmdir helper
init: add an init_unlink helper
init: add an init_umount helper
init: add an init_mount helper
init: mark create_dev as __init
init: mark console_on_rootfs as __init
init: initialize ramdisk_execute_command at compile time
devtmpfs: refactor devtmpfsd()
...
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git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux
Pull close_range() implementation from Christian Brauner:
"This adds the close_range() syscall. It allows to efficiently close a
range of file descriptors up to all file descriptors of a calling
task.
This is coordinated with the FreeBSD folks which have copied our
version of this syscall and in the meantime have already merged it in
April 2019:
https://reviews.freebsd.org/D21627
https://svnweb.freebsd.org/base?view=revision&revision=359836
The syscall originally came up in a discussion around the new mount
API and making new file descriptor types cloexec by default. During
this discussion, Al suggested the close_range() syscall.
First, it helps to close all file descriptors of an exec()ing task.
This can be done safely via (quoting Al's example from [1] verbatim):
/* that exec is sensitive */
unshare(CLONE_FILES);
/* we don't want anything past stderr here */
close_range(3, ~0U);
execve(....);
The code snippet above is one way of working around the problem that
file descriptors are not cloexec by default. This is aggravated by the
fact that we can't just switch them over without massively regressing
userspace. For a whole class of programs having an in-kernel method of
closing all file descriptors is very helpful (e.g. demons, service
managers, programming language standard libraries, container managers
etc.).
Second, it allows userspace to avoid implementing closing all file
descriptors by parsing through /proc/<pid>/fd/* and calling close() on
each file descriptor and other hacks. From looking at various
large(ish) userspace code bases this or similar patterns are very
common in service managers, container runtimes, and programming
language runtimes/standard libraries such as Python or Rust.
In addition, the syscall will also work for tasks that do not have
procfs mounted and on kernels that do not have procfs support compiled
in. In such situations the only way to make sure that all file
descriptors are closed is to call close() on each file descriptor up
to UINT_MAX or RLIMIT_NOFILE, OPEN_MAX trickery.
Based on Linus' suggestion close_range() also comes with a new flag
CLOSE_RANGE_UNSHARE to more elegantly handle file descriptor dropping
right before exec. This would usually be expressed in the sequence:
unshare(CLONE_FILES);
close_range(3, ~0U);
as pointed out by Linus it might be desirable to have this be a part
of close_range() itself under a new flag CLOSE_RANGE_UNSHARE which
gets especially handy when we're closing all file descriptors above a
certain threshold.
Test-suite as always included"
* tag 'close-range-v5.9' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
tests: add CLOSE_RANGE_UNSHARE tests
close_range: add CLOSE_RANGE_UNSHARE
tests: add close_range() tests
arch: wire-up close_range()
open: add close_range()
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Fold it into the only remaining caller.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
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Expand __receive_fd() with support for replace_fd() for the coming seccomp
"addfd" ioctl(). Add new wrapper receive_fd_replace() for the new behavior
and update existing wrappers to retain old behavior.
Thanks to Colin Ian King <colin.king@canonical.com> for pointing out an
uninitialized variable exposure in an earlier version of this patch.
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Dmitry Kadashev <dkadashev@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Sargun Dhillon <sargun@sargun.me>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
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For both pidfd and seccomp, the __user pointer is not used. Update
__receive_fd() to make writing to ufd optional via a NULL check. However,
for the receive_fd_user() wrapper, ufd is NULL checked so an -EFAULT
can be returned to avoid changing the SCM_RIGHTS interface behavior. Add
new wrapper receive_fd() for pidfd and seccomp that does not use the ufd
argument. For the new helper, the allocated fd needs to be returned on
success. Update the existing callers to handle it.
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Sargun Dhillon <sargun@sargun.me>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
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In preparation for users of the "install a received file" logic outside
of net/ (pidfd and seccomp), relocate and rename __scm_install_fd() from
net/core/scm.c to __receive_fd() in fs/file.c, and provide a wrapper
named receive_fd_user(), as future patches will change the interface
to __receive_fd().
Additionally add a comment to fd_install() as a counterpoint to how
__receive_fd() interacts with fput().
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Dmitry Kadashev <dkadashev@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Sargun Dhillon <sargun@sargun.me>
Cc: Ido Schimmel <idosch@idosch.org>
Cc: Ioana Ciornei <ioana.ciornei@nxp.com>
Cc: linux-fsdevel@vger.kernel.org
Cc: netdev@vger.kernel.org
Reviewed-by: Sargun Dhillon <sargun@sargun.me>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
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One of the use-cases of close_range() is to drop file descriptors just before
execve(). This would usually be expressed in the sequence:
unshare(CLONE_FILES);
close_range(3, ~0U);
as pointed out by Linus it might be desirable to have this be a part of
close_range() itself under a new flag CLOSE_RANGE_UNSHARE.
This expands {dup,unshare)_fd() to take a max_fds argument that indicates the
maximum number of file descriptors to copy from the old struct files. When the
user requests that all file descriptors are supposed to be closed via
close_range(min, max) then we can cap via unshare_fd(min) and hence don't need
to do any of the heavy fput() work for everything above min.
The patch makes it so that if CLOSE_RANGE_UNSHARE is requested and we do in
fact currently share our file descriptor table we create a new private copy.
We then close all fds in the requested range and finally after we're done we
install the new fd table.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
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This adds the close_range() syscall. It allows to efficiently close a range
of file descriptors up to all file descriptors of a calling task.
I was contacted by FreeBSD as they wanted to have the same close_range()
syscall as we proposed here. We've coordinated this and in the meantime, Kyle
was fast enough to merge close_range() into FreeBSD already in April:
https://reviews.freebsd.org/D21627
https://svnweb.freebsd.org/base?view=revision&revision=359836
and the current plan is to backport close_range() to FreeBSD 12.2 (cf. [2])
once its merged in Linux too. Python is in the process of switching to
close_range() on FreeBSD and they are waiting on us to merge this to switch on
Linux as well: https://bugs.python.org/issue38061
The syscall came up in a recent discussion around the new mount API and
making new file descriptor types cloexec by default. During this
discussion, Al suggested the close_range() syscall (cf. [1]). Note, a
syscall in this manner has been requested by various people over time.
First, it helps to close all file descriptors of an exec()ing task. This
can be done safely via (quoting Al's example from [1] verbatim):
/* that exec is sensitive */
unshare(CLONE_FILES);
/* we don't want anything past stderr here */
close_range(3, ~0U);
execve(....);
The code snippet above is one way of working around the problem that file
descriptors are not cloexec by default. This is aggravated by the fact that
we can't just switch them over without massively regressing userspace. For
a whole class of programs having an in-kernel method of closing all file
descriptors is very helpful (e.g. demons, service managers, programming
language standard libraries, container managers etc.).
(Please note, unshare(CLONE_FILES) should only be needed if the calling
task is multi-threaded and shares the file descriptor table with another
thread in which case two threads could race with one thread allocating file
descriptors and the other one closing them via close_range(). For the
general case close_range() before the execve() is sufficient.)
Second, it allows userspace to avoid implementing closing all file
descriptors by parsing through /proc/<pid>/fd/* and calling close() on each
file descriptor. From looking at various large(ish) userspace code bases
this or similar patterns are very common in:
- service managers (cf. [4])
- libcs (cf. [6])
- container runtimes (cf. [5])
- programming language runtimes/standard libraries
- Python (cf. [2])
- Rust (cf. [7], [8])
As Dmitry pointed out there's even a long-standing glibc bug about missing
kernel support for this task (cf. [3]).
In addition, the syscall will also work for tasks that do not have procfs
mounted and on kernels that do not have procfs support compiled in. In such
situations the only way to make sure that all file descriptors are closed
is to call close() on each file descriptor up to UINT_MAX or RLIMIT_NOFILE,
OPEN_MAX trickery (cf. comment [8] on Rust).
The performance is striking. For good measure, comparing the following
simple close_all_fds() userspace implementation that is essentially just
glibc's version in [6]:
static int close_all_fds(void)
{
int dir_fd;
DIR *dir;
struct dirent *direntp;
dir = opendir("/proc/self/fd");
if (!dir)
return -1;
dir_fd = dirfd(dir);
while ((direntp = readdir(dir))) {
int fd;
if (strcmp(direntp->d_name, ".") == 0)
continue;
if (strcmp(direntp->d_name, "..") == 0)
continue;
fd = atoi(direntp->d_name);
if (fd == dir_fd || fd == 0 || fd == 1 || fd == 2)
continue;
close(fd);
}
closedir(dir);
return 0;
}
to close_range() yields:
1. closing 4 open files:
- close_all_fds(): ~280 us
- close_range(): ~24 us
2. closing 1000 open files:
- close_all_fds(): ~5000 us
- close_range(): ~800 us
close_range() is designed to allow for some flexibility. Specifically, it
does not simply always close all open file descriptors of a task. Instead,
callers can specify an upper bound.
This is e.g. useful for scenarios where specific file descriptors are
created with well-known numbers that are supposed to be excluded from
getting closed.
For extra paranoia close_range() comes with a flags argument. This can e.g.
be used to implement extension. Once can imagine userspace wanting to stop
at the first error instead of ignoring errors under certain circumstances.
There might be other valid ideas in the future. In any case, a flag
argument doesn't hurt and keeps us on the safe side.
From an implementation side this is kept rather dumb. It saw some input
from David and Jann but all nonsense is obviously my own!
- Errors to close file descriptors are currently ignored. (Could be changed
by setting a flag in the future if needed.)
- __close_range() is a rather simplistic wrapper around __close_fd().
My reasoning behind this is based on the nature of how __close_fd() needs
to release an fd. But maybe I misunderstood specifics:
We take the files_lock and rcu-dereference the fdtable of the calling
task, we find the entry in the fdtable, get the file and need to release
files_lock before calling filp_close().
In the meantime the fdtable might have been altered so we can't just
retake the spinlock and keep the old rcu-reference of the fdtable
around. Instead we need to grab a fresh reference to the fdtable.
If my reasoning is correct then there's really no point in fancyfying
__close_range(): We just need to rcu-dereference the fdtable of the
calling task once to cap the max_fd value correctly and then go on
calling __close_fd() in a loop.
/* References */
[1]: https://lore.kernel.org/lkml/20190516165021.GD17978@ZenIV.linux.org.uk/
[2]: https://github.com/python/cpython/blob/9e4f2f3a6b8ee995c365e86d976937c141d867f8/Modules/_posixsubprocess.c#L220
[3]: https://sourceware.org/bugzilla/show_bug.cgi?id=10353#c7
[4]: https://github.com/systemd/systemd/blob/5238e9575906297608ff802a27e2ff9effa3b338/src/basic/fd-util.c#L217
[5]: https://github.com/lxc/lxc/blob/ddf4b77e11a4d08f09b7b9cd13e593f8c047edc5/src/lxc/start.c#L236
[6]: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/grantpt.c;h=2030e07fa6e652aac32c775b8c6e005844c3c4eb;hb=HEAD#l17
Note that this is an internal implementation that is not exported.
Currently, libc seems to not provide an exported version of this
because of missing kernel support to do this.
Note, in a recent patch series Florian made grantpt() a nop thereby
removing the code referenced here.
[7]: https://github.com/rust-lang/rust/issues/12148
[8]: https://github.com/rust-lang/rust/blob/5f47c0613ed4eb46fca3633c1297364c09e5e451/src/libstd/sys/unix/process2.rs#L303-L308
Rust's solution is slightly different but is equally unperformant.
Rust calls getdtablesize() which is a glibc library function that
simply returns the current RLIMIT_NOFILE or OPEN_MAX values. Rust then
goes on to call close() on each fd. That's obviously overkill for most
tasks. Rarely, tasks - especially non-demons - hit RLIMIT_NOFILE or
OPEN_MAX.
Let's be nice and assume an unprivileged user with RLIMIT_NOFILE set
to 1024. Even in this case, there's a very high chance that in the
common case Rust is calling the close() syscall 1021 times pointlessly
if the task just has 0, 1, and 2 open.
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Kyle Evans <self@kyle-evans.net>
Cc: Jann Horn <jannh@google.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Dmitry V. Levin <ldv@altlinux.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: linux-api@vger.kernel.org
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cpy and set really should be size_t; we won't get an overflow on that,
since sysctl_nr_open can't be set above ~(size_t)0 / sizeof(void *),
so nr that would've managed to overflow size_t on that multiplication
won't get anywhere near copy_fdtable() - we'll fail with EMFILE
before that.
Cc: stable@kernel.org # v2.6.25+
Fixes: 9cfe015aa424 (get rid of NR_OPEN and introduce a sysctl_nr_open)
Reported-by: Thiago Macieira <thiago.macieira@intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Dmitry reports that a test case shows that io_uring isn't honoring a
modified rlimit nofile setting. get_unused_fd_flags() checks the task
signal->rlimi[] for the limits. As this isn't easily inheritable,
provide a __get_unused_fd_flags() that takes the value instead. Then we
can grab it when the request is prepared (from the original task), and
pass that in when we do the async part part of the open.
Reported-by: Dmitry Kadashev <dkadashev@gmail.com>
Tested-by: Dmitry Kadashev <dkadashev@gmail.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux
Pull thread management updates from Christian Brauner:
"Sargun Dhillon over the last cycle has worked on the pidfd_getfd()
syscall.
This syscall allows for the retrieval of file descriptors of a process
based on its pidfd. A task needs to have ptrace_may_access()
permissions with PTRACE_MODE_ATTACH_REALCREDS (suggested by Oleg and
Andy) on the target.
One of the main use-cases is in combination with seccomp's user
notification feature. As a reminder, seccomp's user notification
feature was made available in v5.0. It allows a task to retrieve a
file descriptor for its seccomp filter. The file descriptor is usually
handed of to a more privileged supervising process. The supervisor can
then listen for syscall events caught by the seccomp filter of the
supervisee and perform actions in lieu of the supervisee, usually
emulating syscalls. pidfd_getfd() is needed to expand its uses.
There are currently two major users that wait on pidfd_getfd() and one
future user:
- Netflix, Sargun said, is working on a service mesh where users
should be able to connect to a dns-based VIP. When a user connects
to e.g. 1.2.3.4:80 that runs e.g. service "foo" they will be
redirected to an envoy process. This service mesh uses seccomp user
notifications and pidfd to intercept all connect calls and instead
of connecting them to 1.2.3.4:80 connects them to e.g.
127.0.0.1:8080.
- LXD uses the seccomp notifier heavily to intercept and emulate
mknod() and mount() syscalls for unprivileged containers/processes.
With pidfd_getfd() more uses-cases e.g. bridging socket connections
will be possible.
- The patchset has also seen some interest from the browser corner.
Right now, Firefox is using a SECCOMP_RET_TRAP sandbox managed by a
broker process. In the future glibc will start blocking all signals
during dlopen() rendering this type of sandbox impossible. Hence,
in the future Firefox will switch to a seccomp-user-nofication
based sandbox which also makes use of file descriptor retrieval.
The thread for this can be found at
https://sourceware.org/ml/libc-alpha/2019-12/msg00079.html
With pidfd_getfd() it is e.g. possible to bridge socket connections
for the supervisee (binding to a privileged port) and taking actions
on file descriptors on behalf of the supervisee in general.
Sargun's first version was using an ioctl on pidfds but various people
pushed for it to be a proper syscall which he duely implemented as
well over various review cycles. Selftests are of course included.
I've also added instructions how to deal with merge conflicts below.
There's also a small fix coming from the kernel mentee project to
correctly annotate struct sighand_struct with __rcu to fix various
sparse warnings. We've received a few more such fixes and even though
they are mostly trivial I've decided to postpone them until after -rc1
since they came in rather late and I don't want to risk introducing
build warnings.
Finally, there's a new prctl() command PR_{G,S}ET_IO_FLUSHER which is
needed to avoid allocation recursions triggerable by storage drivers
that have userspace parts that run in the IO path (e.g. dm-multipath,
iscsi, etc). These allocation recursions deadlock the device.
The new prctl() allows such privileged userspace components to avoid
allocation recursions by setting the PF_MEMALLOC_NOIO and
PF_LESS_THROTTLE flags. The patch carries the necessary acks from the
relevant maintainers and is routed here as part of prctl()
thread-management."
* tag 'threads-v5.6' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
prctl: PR_{G,S}ET_IO_FLUSHER to support controlling memory reclaim
sched.h: Annotate sighand_struct with __rcu
test: Add test for pidfd getfd
arch: wire up pidfd_getfd syscall
pid: Implement pidfd_getfd syscall
vfs, fdtable: Add fget_task helper
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Just one caller of this, and just use filp_close() there manually.
This is important to allow async close/removal of the fd.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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This introduces a function which can be used to fetch a file, given an
arbitrary task. As long as the user holds a reference (refcnt) to the
task_struct it is safe to call, and will either return NULL on failure,
or a pointer to the file, with a refcnt.
This patch is based on Oleg Nesterov's (cf. [1]) patch from September
2018.
[1]: Link: https://lore.kernel.org/r/20180915160423.GA31461@redhat.com
Signed-off-by: Sargun Dhillon <sargun@sargun.me>
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20200107175927.4558-2-sargun@sargun.me
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
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This reverts commit 8243186f0cc7 ("fs: remove ksys_dup()") and the
subsequent fix for it in commit 2d3145f8d280 ("early init: fix error
handling when opening /dev/console").
Trying to use filp_open() and f_dupfd() instead of pseudo-syscalls
caused more trouble than what is worth it: it requires accessing vfs
internals and it turns out there were other bugs in it too.
In particular, the file reference counting was wrong - because unlike
the original "open+2*dup" sequence it used "filp_open+3*f_dupfd" and
thus had an extra leaked file reference.
That in turn then caused odd problems with Androidx86 long after boot
becaue of how the extra reference to the console kept the session active
even after all file descriptors had been closed.
Reported-by: youling 257 <youling257@gmail.com>
Cc: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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ksys_dup() is used only at one place in the kernel, namely to duplicate
fd 0 of /dev/console to stdout and stderr. The same functionality can be
achieved by using functions already available within the kernel namespace.
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
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This reverts commit 0be0ee71816b2b6725e2b4f32ad6726c9d729777.
I was hoping it would be benign to switch over entirely to FMODE_STREAM,
and we'd have just a couple of small fixups we'd need, but it looks like
we're not quite there yet.
While it worked fine on both my desktop and laptop, they are fairly
similar in other respects, and run mostly the same loads. Kenneth
Crudup reports that it seems to break both his vmware installation and
the KDE upower service. In both cases apparently leading to timeouts
due to waitinmg for the f_pos lock.
There are a number of character devices in particular that definitely
want stream-like behavior, but that currently don't get marked as
streams, and as a result get the exclusion between concurrent
read()/write() on the same file descriptor. Which doesn't work well for
them.
The most obvious example if this is /dev/console and /dev/tty, which use
console_fops and tty_fops respectively (and ptmx_fops for the pty master
side). It may be that it's just this that causes problems, but we
clearly weren't ready yet.
Because there's a number of other likely common cases that don't have
llseek implementations and would seem to act as stream devices:
/dev/fuse (fuse_dev_operations)
/dev/mcelog (mce_chrdev_ops)
/dev/mei0 (mei_fops)
/dev/net/tun (tun_fops)
/dev/nvme0 (nvme_dev_fops)
/dev/tpm0 (tpm_fops)
/proc/self/ns/mnt (ns_file_operations)
/dev/snd/pcm* (snd_pcm_f_ops[])
and while some of these could be trivially automatically detected by the
vfs layer when the character device is opened by just noticing that they
have no read or write operations either, it often isn't that obvious.
Some character devices most definitely do use the file position, even if
they don't allow seeking: the firmware update code, for example, uses
simple_read_from_buffer() that does use f_pos, but doesn't allow seeking
back and forth.
We'll revisit this when there's a better way to detect the problem and
fix it (possibly with a coccinelle script to do more of the FMODE_STREAM
annotations).
Reported-by: Kenneth R. Crudup <kenny@panix.com>
Cc: Kirill Smelkov <kirr@nexedi.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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fdget_pos() is used by file operations that will read and update f_pos:
things like "read()", "write()" and "lseek()" (but not, for example,
"pread()/pwrite" that get their file positions elsewhere).
However, it had two separate escape clauses for this, because not
everybody wants or needs serialization of the file position.
The first and most obvious case is the "file descriptor doesn't have a
position at all", ie a stream-like file. Except we didn't actually use
FMODE_STREAM, but instead used FMODE_ATOMIC_POS. The reason for that
was that FMODE_STREAM didn't exist back in the days, but also that we
didn't want to mark all the special cases, so we only marked the ones
that _required_ position atomicity according to POSIX - regular files
and directories.
The case one was intentionally lazy, but now that we _do_ have
FMODE_STREAM we could and should just use it. With the change to use
FMODE_STREAM, there are no remaining uses for FMODE_ATOMIC_POS, and all
the code to set it is deleted.
Any cases where we don't want the serialization because the driver (or
subsystem) doesn't use the file position should just be updated to do
"stream_open()". We've done that for all the obvious and common
situations, we may need a few more. Quoting Kirill Smelkov in the
original FMODE_STREAM thread (see link below for full email):
"And I appreciate if people could help at least somehow with "getting
rid of mixed case entirely" (i.e. always lock f_pos_lock on
!FMODE_STREAM), because this transition starts to diverge from my
particular use-case too far. To me it makes sense to do that
transition as follows:
- convert nonseekable_open -> stream_open via stream_open.cocci;
- audit other nonseekable_open calls and convert left users that
truly don't depend on position to stream_open;
- extend stream_open.cocci to analyze alloc_file_pseudo as well (this
will cover pipes and sockets), or maybe convert pipes and sockets
to FMODE_STREAM manually;
- extend stream_open.cocci to analyze file_operations that use
no_llseek or noop_llseek, but do not use nonseekable_open or
alloc_file_pseudo. This might find files that have stream semantic
but are opened differently;
- extend stream_open.cocci to analyze file_operations whose
.read/.write do not use ppos at all (independently of how file was
opened);
- ...
- after that remove FMODE_ATOMIC_POS and always take f_pos_lock if
!FMODE_STREAM;
- gather bug reports for deadlocked read/write and convert missed
cases to FMODE_STREAM, probably extending stream_open.cocci along
the road to catch similar cases
i.e. always take f_pos_lock unless a file is explicitly marked as
being stream, and try to find and cover all files that are streams"
We have not done the "extend stream_open.cocci to analyze
alloc_file_pseudo" as well, but the previous commit did manually handle
the case of pipes and sockets.
The other case where we can avoid locking f_pos is the "this file
descriptor only has a single user and it is us, and thus there is no
need to lock it".
The second test was correct, although a bit subtle and worth just
re-iterating here. There are two kinds of other sources of references
to the same file descriptor: file descriptors that have been explicitly
shared across fork() or with dup(), and file tables having elevated
reference counts due to threading (or explicit file sharing with
clone()).
The first case would have incremented the file count explicitly, and in
the second case the previous __fdget() would have incremented it for us
and set the FDPUT_FPUT flag.
But in both cases the file count would be greater than one, so the
"file_count(file) > 1" test catches both situations. Also note that if
file_count is 1, that also means that no other thread can have access to
the file table, so there also cannot be races with concurrent calls to
dup()/fork()/clone() that would increment the file count any other way.
Link: https://lore.kernel.org/linux-fsdevel/20190413184404.GA13490@deco.navytux.spb.ru
Cc: Kirill Smelkov <kirr@nexedi.com>
Cc: Eic Dumazet <edumazet@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Marco Elver <elver@google.com>
Cc: Andrea Parri <parri.andrea@gmail.com>
Cc: Paul McKenney <paulmck@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Pull io_uring IO interface from Jens Axboe:
"Second attempt at adding the io_uring interface.
Since the first one, we've added basic unit testing of the three
system calls, that resides in liburing like the other unit tests that
we have so far. It'll take a while to get full coverage of it, but
we're working towards it. I've also added two basic test programs to
tools/io_uring. One uses the raw interface and has support for all the
various features that io_uring supports outside of standard IO, like
fixed files, fixed IO buffers, and polled IO. The other uses the
liburing API, and is a simplified version of cp(1).
This adds support for a new IO interface, io_uring.
io_uring allows an application to communicate with the kernel through
two rings, the submission queue (SQ) and completion queue (CQ) ring.
This allows for very efficient handling of IOs, see the v5 posting for
some basic numbers:
https://lore.kernel.org/linux-block/20190116175003.17880-1-axboe@kernel.dk/
Outside of just efficiency, the interface is also flexible and
extendable, and allows for future use cases like the upcoming NVMe
key-value store API, networked IO, and so on. It also supports async
buffered IO, something that we've always failed to support in the
kernel.
Outside of basic IO features, it supports async polled IO as well.
This particular feature has already been tested at Facebook months ago
for flash storage boxes, with 25-33% improvements. It makes polled IO
actually useful for real world use cases, where even basic flash sees
a nice win in terms of efficiency, latency, and performance. These
boxes were IOPS bound before, now they are not.
This series adds three new system calls. One for setting up an
io_uring instance (io_uring_setup(2)), one for submitting/completing
IO (io_uring_enter(2)), and one for aux functions like registrating
file sets, buffers, etc (io_uring_register(2)). Through the help of
Arnd, I've coordinated the syscall numbers so merge on that front
should be painless.
Jon did a writeup of the interface a while back, which (except for
minor details that have been tweaked) is still accurate. Find that
here:
https://lwn.net/Articles/776703/
Huge thanks to Al Viro for helping getting the reference cycle code
correct, and to Jann Horn for his extensive reviews focused on both
security and bugs in general.
There's a userspace library that provides basic functionality for
applications that don't need or want to care about how to fiddle with
the rings directly. It has helpers to allow applications to easily set
up an io_uring instance, and submit/complete IO through it without
knowing about the intricacies of the rings. It also includes man pages
(thanks to Jeff Moyer), and will continue to grow support helper
functions and features as time progresses. Find it here:
git://git.kernel.dk/liburing
Fio has full support for the raw interface, both in the form of an IO
engine (io_uring), but also with a small test application (t/io_uring)
that can exercise and benchmark the interface"
* tag 'io_uring-2019-03-06' of git://git.kernel.dk/linux-block:
io_uring: add a few test tools
io_uring: allow workqueue item to handle multiple buffered requests
io_uring: add support for IORING_OP_POLL
io_uring: add io_kiocb ref count
io_uring: add submission polling
io_uring: add file set registration
net: split out functions related to registering inflight socket files
io_uring: add support for pre-mapped user IO buffers
block: implement bio helper to add iter bvec pages to bio
io_uring: batch io_kiocb allocation
io_uring: use fget/fput_many() for file references
fs: add fget_many() and fput_many()
io_uring: support for IO polling
io_uring: add fsync support
Add io_uring IO interface
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(Taken from https://bugzilla.kernel.org/show_bug.cgi?id=200647)
'get_unused_fd_flags' in kthread cause kernel crash. It works fine on
4.1, but causes crash after get 64 fds. It also cause crash on
ubuntu1404/1604/1804, centos7.5, and the crash messages are almost the
same.
The crash message on centos7.5 shows below:
start fd 61
start fd 62
start fd 63
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: __wake_up_common+0x2e/0x90
PGD 0
Oops: 0000 [#1] SMP
Modules linked in: test(OE) xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ipt_REJECT nf_reject_ipv4 tun bridge stp llc ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter devlink sunrpc kvm_intel kvm irqbypass crc32_pclmul ghash_clmulni_intel aesni_intel lrw gf128mul glue_helper ablk_helper cryptd sg ppdev pcspkr virtio_balloon parport_pc parport i2c_piix4 joydev ip_tables xfs libcrc32c sr_mod cdrom sd_mod crc_t10dif crct10dif_generic ata_generic pata_acpi virtio_scsi virtio_console virtio_net cirrus drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm crct10dif_pclmul crct10dif_common crc32c_intel drm ata_piix serio_raw libata virtio_pci virtio_ring i2c_core
virtio floppy dm_mirror dm_region_hash dm_log dm_mod
CPU: 2 PID: 1820 Comm: test_fd Kdump: loaded Tainted: G OE ------------ 3.10.0-862.3.3.el7.x86_64 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.10.2-0-g5f4c7b1-prebuilt.qemu-project.org 04/01/2014
task: ffff8e92b9431fa0 ti: ffff8e94247a0000 task.ti: ffff8e94247a0000
RIP: 0010:__wake_up_common+0x2e/0x90
RSP: 0018:ffff8e94247a2d18 EFLAGS: 00010086
RAX: 0000000000000000 RBX: ffffffff9d09daa0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffffffff9d09daa0
RBP: ffff8e94247a2d50 R08: 0000000000000000 R09: ffff8e92b95dfda8
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff9d09daa8
R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000003
FS: 0000000000000000(0000) GS:ffff8e9434e80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000017c686000 CR4: 00000000000207e0
Call Trace:
__wake_up+0x39/0x50
expand_files+0x131/0x250
__alloc_fd+0x47/0x170
get_unused_fd_flags+0x30/0x40
test_fd+0x12a/0x1c0 [test]
kthread+0xd1/0xe0
ret_from_fork_nospec_begin+0x21/0x21
Code: 66 90 55 48 89 e5 41 57 41 89 f7 41 56 41 89 ce 41 55 41 54 49 89 fc 49 83 c4 08 53 48 83 ec 10 48 8b 47 08 89 55 cc 4c 89 45 d0 <48> 8b 08 49 39 c4 48 8d 78 e8 4c 8d 69 e8 75 08 eb 3b 4c 89 ef
RIP __wake_up_common+0x2e/0x90
RSP <ffff8e94247a2d18>
CR2: 0000000000000000
This issue exists since CentOS 7.5 3.10.0-862 and CentOS 7.4
(3.10.0-693.21.1 ) is ok. Root cause: the item 'resize_wait' is not
initialized before being used.
Reported-by: Richard Zhang <zhang.zijian@h3c.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Some uses cases repeatedly get and put references to the same file, but
the only exposed interface is doing these one at the time. As each of
these entail an atomic inc or dec on a shared structure, that cost can
add up.
Add fget_many(), which works just like fget(), except it takes an
argument for how many references to get on the file. Ditto fput_many(),
which can drop an arbitrary number of references to a file.
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc
Pull char/misc driver updates from Greg KH:
"Here is the big set of char and misc driver patches for 4.21-rc1.
Lots of different types of driver things in here, as this tree seems
to be the "collection of various driver subsystems not big enough to
have their own git tree" lately.
Anyway, some highlights of the changes in here:
- binderfs: is it a rule that all driver subsystems will eventually
grow to have their own filesystem? Binder now has one to handle the
use of it in containerized systems.
This was discussed at the Plumbers conference a few months ago and
knocked into mergable shape very fast by Christian Brauner. Who
also has signed up to be another binder maintainer, showing a
distinct lack of good judgement :)
- binder updates and fixes
- mei driver updates
- fpga driver updates and additions
- thunderbolt driver updates
- soundwire driver updates
- extcon driver updates
- nvmem driver updates
- hyper-v driver updates
- coresight driver updates
- pvpanic driver additions and reworking for more device support
- lp driver updates. Yes really, it's _finally_ moved to the proper
parallal port driver model, something I never thought I would see
happen. Good stuff.
- other tiny driver updates and fixes.
All of these have been in linux-next for a while with no reported
issues"
* tag 'char-misc-4.21-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc: (116 commits)
MAINTAINERS: add another Android binder maintainer
intel_th: msu: Fix an off-by-one in attribute store
stm class: Add a reference to the SyS-T document
stm class: Fix a module refcount leak in policy creation error path
char: lp: use new parport device model
char: lp: properly count the lp devices
char: lp: use first unused lp number while registering
char: lp: detach the device when parallel port is removed
char: lp: introduce list to save port number
bus: qcom: remove duplicated include from qcom-ebi2.c
VMCI: Use memdup_user() rather than duplicating its implementation
char/rtc: Use of_node_name_eq for node name comparisons
misc: mic: fix a DMA pool free failure
ptp: fix an IS_ERR() vs NULL check
genwq |
